The invention pertains to drilling and rock excavation as well as drilling for exploration, for mining or mineral development and for sampling and monitoring wells, and for gas, oil, and water wells. In addition, the mining industry, the dimension stone industry, the construction industry, the oil and gas industry, and any other industries that are involved in the drilling, cutting, and grinding of rock, coal, or concrete or in tunneling through rock may utilize this invention. Furthermore, the invention should also be applicable to the cutting, drilling, and grinding of other materials including metals, ceramics, other refractory materials, and also biological caries as in dental drilling of teeth.
Drilling and rock excavation represent a significant segment of the total mining system, and yearly drilling costs for five segments of the mining industry, namely copper/molybdenum, iron/titanium, lead/zinc, gold/silver, and crushed/dimension stone in the United States are about 1.5 billion dollars.
Drill bit costs represent about 600 million dollars per year or about 40 percent of the total drilling costs. Increasing the bit life by 100 percent can translate into yearly savings of 300 million dollars in drill bit costs.
Significant savings could be achieved if a method is devised for greatly enhancing the total penetration and the penetration rate of rock drilling and tunneling systems as well as greatly enhancing the rate of cutting and grinding of rocks while simultaneously extending the life of the bits, cutting tools and grinding media.
Therefore, significant savings could be realized in general drilling costs if a method is devised which allows increased drilling rates at constant applied mechanical stress during the drilling or tunneling, but prevents bit or blade wear.
Known in the prior art are methods of maintaining the properties and parameters of a drilling fluid by introducing chemical agents into the drilling fluid while it circulates in a well. Mamadzhanov et al in U.S. Pat. No. 4,410,052, issued Oct. 18, 1983, maintain the well integrity by adjusting the redox potential of the flushing fluid to the value determined at the moment of tapping the bed rock. This eliminates the ion exchange reactions between the bed walls and the flushing fluid and therefore maintains the natural permeability of the oil or gas productive well. This method is not concerned with enhancing drilling for excavation. Mamadzhanov et al in U.S. Pat. No. 4,385,666, issued May 31 1983, maintain and control the properties and parameters of drilling muds by adjusting their oxidation/reduction potential (redox) at preset values. This is done to maintain the rheological stability of the drilling mud which often gets diluted and changed in composition by ion exchange reactions in deep oil and gas well drilling and not to enhance the drilling rate or prolonging the drill bit life. Alekhin et al in U.S. Pat. No. 4,342,222, issued Aug. 3, 1982, used the redox potential of the drilling mud to determine the depth of a fluid-saturated stratum and the type of fluid such as mineralized water, oil, or gas released. Mixing the drilling mud with any of these fluid types changes its redox potential in a given direction, which identifies the nature of the fluid. This does not effect enhanced drilling productivity. Johnson and Kelly in U.S. Pat. No. 3,307,625, issued Mar. 7, 1967, pertains to wells formed when a subsurface source of hydrogen sulfide (H.sub.2 S) is encountered. Liberation of H.sub.2 S (a weak acid) can lower the pH of water to a point where the drill metal starts to corrode. To prevent this corrosion, they added an alkali metal hydroxide or sulfide, e.g., NaOH or Na.sub.2 S to raise the pH of the drilling fluid to the 7 to 9 range. None of the prior art mentioned above are pertinent to increasing drilling productivity.
It has been found that maximum increases in penetration can be obtained simultaneously with maximum increases in bit life using concentrations of chemical additive solutions, such as cationic organic surfactant and inorganic salt solutions, that neutralize the naturally-occurring negative charge on the rock surface, thereby producing a zero zeta potential or zero surface charge (ZSC) condition (cf., Engelmann,W.H., P.J. Watson, P.A. Tuzinski, and J.E. Pahlman. Zeta Potential Control for Simultaneous Enhancement of Penetration Rates and Bit Life in Rock Drilling. BuMines RI 9103, 1987, 24pp, and Zeta Potential Control for Enhancement Drilling of Taconite and Other Hard Rocks, Proceedings of the 60th Annual Meeting of the Minnesota Section, AIME and 48th Annual Mining Symposium, pp.6-1 to 6-22; and Khalafalla, S. E., W. H. Engelmann, and J. E. Pahlman. Isoelectric Drilling Method. U.S. Pat. Application Ser. No. 5,041, filed Jan. 15, 1987, now U.S. Pat. No. 4,765,415.)
The present invention provides a means for enhancing drilling rates while also prolonging the bit life at constant applied mechanical stress during drilling operations. This is accomplished by virtue of the invention's discovery that enhanced drilling rates are a function of the rock surface condition, and that, if the rock surface is maintained at the zero point of charge (ZPC), or zero surface charge (ZSC) condition, regardless of the salt type or concentration or water source, enhanced drilling rates coupled with prolongation of the bit life are attained. It has now been determined that water-soluble, nonionic, high-molecular-weight, organic polymers such as the polyalkene oxide class of polymers like polyethylene oxide (PEO) also are able to produce the ZSC condition.